1. Field of the Invention
This invention relates generally to apparatus for pumping fluids and more particularly to apparatus for pumping liquid ink and cleaning fluids to the printing sections of printing machines for corrugated paperboard.
2. Brief Description of the Prior Art
Conventional printing sections utilize anilox and doctor rolls to place a film of ink on a printing plate. Alternatively, doctor blades of various configurations are used in place of a doctor roll in conjunction with the anilox roll and, sometimes, both a doctor roll and a doctor blade are used alternatively in the same printing section. An example of a printing apparatus pertinent to this invention is shown in Wells et al U.S. Pat. No. 5,103,732, the disclosures of which are incorporated herein by reference. This patent shows an anilox/doctor roll configuration as well as an anilox/doctor blade configuration.
A diaphragm pump is the type most commonly used in the corrugated industry. A diaphragm pump utilizes reciprocally operable resilient diaphragms to suck liquid in the bottom of the pump and force it out the top [or vice versa] along with conventional duckbill valves to control the direction of flow. Such pumps are available from Aro Corporation, Aro Center, Bryan, Ohio 43506. Model 666053-021 is typical. This pump is also made in a dual diaphragm model with two inlets and two outlets to provide a right and left side pump.
Currently used pumps usually have only one inlet and one outlet. Therefore, a separate pump is required for each printing section of a machine, it being understood that each section applies a different ink color. Most printing machines have two printing sections, often three, and sometimes four. If it is desired to also pump the excess ink back to the ink supply rather than use a gravity return, then two more separate pumps would be required for each printing section since each printing section has two drains for the ink, one on each side of the printing section. Therefore, even when a dual diaphragm pump is used, only one inlet/outlet is available for pumping excess ink back to the ink supply.
In the operation of printing machines, such as referred to in the aforementioned patent, it is not uncommon to change ink colors several times during a shift because many orders are for short runs. When a color change is made, it is necessary to thoroughly clean the entire ink system, including ink rolls, doctor blades, and supply and drain lines as well as the ink pumps themselves to prevent contamination of the new ink.
A first considerable disadvantage of the diaphragm pump is that it is difficult to clean because of its many parts and surfaces to which the ink adheres. Such pumps are unidirectional and cannot be backwashed so that cleaning is not totally effective besides being time consuming. Backwashing means the ability to run a pump in both forward and reverse directions so that a cleaning fluid can flush ink from the parts that might normally escape cleaning from the cleaning fluid flowing in only one direction.
A second considerable disadvantage is that a relatively large volume of ink remains in the pump and the ink supply line to the pump when the pump is turned off prior to cleaning. With the current cost of ink being about $4.00 to $8.00 per pound, the cost of ink currently wasted in such parts is considerable. In addition, considerable costs are incurred for the wash water or other cleaning fluid because the pumps are difficult to clean.
Another considerable disadvantage of such pumps is that they tend to cause a positive ink pressure in the enclosed chamber of closed-chamber doctor blade systems, causing the ink to leak through the end seals (and sometimes between the doctor blades and anilox roll as well). Ink leaking at the ends of the anilox roll beyond the end seals often results in ink slinging which can damage the product being printed. But, if the ink chamber does not remain full of ink, the ink chamber can go dry, resulting in non-printing and even damage to the anilox roll. Less serious but still troublesome disadvantages are that such pumps tend to deliver the ink in surges rather than in an even flow. And, such pumps are subject to stalling at slow speed, particularly when high viscosity inks are being used.
Accordingly, an object of this invention generally is to overcome the disadvantages of current ink pumps. More particularly, it is an object of this invention to provide a pump that can both pump ink to a printing section and pump excess ink from the printing section.
Another object of this invention is to provide a pump that can be run in a reverse direction to pump ink remaining in the pump, and in the ink supply line between an ink supply and the pump, back to the ink supply.
Another object of this invention is to provide a pump that can be backwashed to more efficiently remove ink remaining therein.
Another object of this invention is to provide a single pump that can be used to pump a different color ink to each of several printing sections simultaneously.
These and other objects and novel features will become more apparent from the following detailed description when read in connection with the accompanying drawings.